This invention relates generally to sewing machines, and, more specifically, to sewing machines having apparatus to ensure a seam is sewn having a correct width.
Sewing machines wherein the instant invention finds exemplary application include industrial sewing machines used to form edge seams. Such machines may incorporate a feedback sensor to ensure proper positioning of material being sewn. A light-based sensor arrangement used in certain commercial sewing machines has a light sensor that is positionable to track a location of an edge of material while the material is being sewn. The sensor can be adjusted to trigger when the sewn seam becomes too wide, occluding the sensor beam. When such a condition occurs, the sensor triggers to turn off the sewing machine. Unfortunately, however, the momentum of the sewing machine causes additional stitches to be sewn in the material before the needle can be brought to a halt. Consequently, from about one to perhaps several inches of noncompliant seam will be sewn as the machine slows down. Generally, the noncompliant portion of the seam must, at a minimum, be picked apart for re-stitching at a correct width. The entire seam may need to be undone, and the seam started from a beginning, for aesthetic or other reasons. In some cases, the noncompliant seam may ruin the article in which the seam is being sewn, causing the article to be scrapped.
Certain available sewing machines have an edge guide to space a sewing machine needle from a material""s sewn edge. Such guides are adjustable mechanically, for example, by turning a threaded shaft, but such adjustment is limited to an initial set-up for seam size. A seam may be sewn by an operator with such a machine by pressing material into engagement with the guide surface simultaneously with pushing slightly in a direction to feed material into the machine needle. No adjustability in guide location is contemplated when a seam is being sewn.
The invention provides a device automatically to adjust a seam size while sewing the seam in a sewing machine. The invention can be embodied as a clamping foot for a sewing machine. The clamping foot includes an inside foot adapted for attachment to the sewing machine, and an outside foot suspended in transversely adjustable relation from the inside foot. A biasing element is typically arranged to bias the outside foot in an outside direction from the inside foot. The clamping foot may be used in combination with an edge guide operable to assist in feeding material into sewing engagement with a sewing machine on which the clamping foot is attached. Usually, a transducer is affixed between the sewing machine and the edge guide. The transducer transversely displaces the edge guide to control a seam size. A sensor is positioned to validate a seam size and provide a signal in a feedback loop to control the transducer. A stop mechanism may be used to limit a maximum transverse displacement of the outside foot in an inside direction.
These features, advantages, and alternative aspects of the present invention will be apparent to those skilled in the art from a consideration of the following detailed description taken in combination with the accompanying drawings.